Many industries have a commercial need to monitor the concentration of particular constituents in a fluid. The oil refining industry, wineries, and the diary industry are examples of industries where fluid testing is routine. In the health care field, people such as diabetics, for example, have a need to monitor a particular constituent within their bodily fluids. A number of systems are available that allow people to test a body fluid, such as, blood, urine, or saliva, to conveniently monitor the level of a particular fluid constituent, such as, for example, cholesterol, proteins, and glucose. Patients suffering from diabetes, a disorder of the pancreas where insufficient insulin production prevents the proper digestion of sugar, have a need to carefully monitor their blood glucose levels on a daily basis. A number of systems that allow people to conveniently monitor their blood glucose levels are available. Such systems typically include a test strip where the user applies a blood sample and a meter that “reads” the test strip to determine the glucose level in the blood sample.
Among the various technologies available for measuring blood glucose levels, electrochemical technologies are particularly desirable because only a very small blood sample may be needed to perform the measurement. In amperometric electrochemical-based systems, the test strip typically includes a sample chamber that contains reagents, such as glucose oxidase and a mediator, and electrodes. When the user applies a blood sample to the sample chamber, the reagents react with the glucose, and the meter applies a voltage to the electrodes to cause a redox reaction. The meter measures the resulting current and calculates the glucose level based on the current. Other systems based on coulometry or voltametry are also known.
Because the test strip includes a biological reagent, every strip manufactured is not reproducible with the exact same sensitivity. Therefore, test strips are manufactured in distinct lots and data particular to that lot is often used as a signal by the meter's microprocessor to assist in accurately performing the meter calculation. The data is used to help accurately correlate the measured current with the actual glucose concentration. For example, the data could represent a numeric code that “signals” the meter's microprocessor to access and utilize a specific set of stored calibration values from an on-board memory device during calculation.
In past systems, the code particular to a specific lot of strips has been input into the meter manually by the user, or connected through some type of memory device (such as a ROM chip) packaged along with test strips from a single manufacturing lot. This step of manual input, or connection by the user, adds to the risk of improperly inputting the wrong code data. Such errors can lead to inaccurate measurements and an improper recording of the patient's history. Past systems have also included bar-code readable information incorporated onto individual strips. Individually imprinting a particular bar-code on each strip adds significant manufacturing costs to the strip production and requires the additional expense of a bar-code reader incorporated within the meter in order to obtain the information.
It should be emphasized that accurate measurements of concentration levels in a body fluid, such as blood, may be critical to the long-term health of many users. As a result, there is a need for a high level of reliability in the meters and test strips used to measure concentration levels in fluids. Thus, it is desirable to have a cost effective auto-calibration system for diagnostic test strips that more reliably and more accurately provides a signaling code for individual test strips.